I also have this problem for all the sites I administer. I select "View Last Logins" at the top of Admin and I get the warning "You do not have sufficient permissions to access this page", though, in the "Sucuri WordPress Integrity Checks", "List all administrator users and their latest login time" still lists the admins logins.

Updated to Version 1.4.7 and all Last Logins disappeared.
Also, when you click the blue "Show All Results" button on the "Sucuri Plugin Last-Logins" window, no Last Logins appear and... the button itself disappears!

There is no blue-highlighted view last logins message when entering admin, as well.

The above issue persists, though this is not a major concern as all other functions of the plugin are operating well.

I have logged in/out on my own site 6 times and the other sites I administer twice each, yet there is no change.

Also, the "Sucuri WordPress Integrity Checks" section "Administrator Users" lists Username and Email, but no IP Address or Date & Time. There is only one entry, mine, even though on my site I have logged in/out 6 times.

The blue "Show All Results" button on the "Sucuri Plugin Last-Logins" window still disappears when clicked.

I disabled all the other plugins on my site, cleared cache, and logged out/in twice, but no change.